LIMITS(3) | Library Functions Manual | LIMITS(3)

# NAME

limits — standard limits

# SYNOPSIS

#include <limits.h>

# DESCRIPTION

The <limits.h> header defines various compile-time and runtime limits. These can be grouped into three categories:

1. Compile-time limits defined in a header file.
2. Runtime system limits that are not associated with a file or directory; see sysconf(3).
3. Runtime limits that are associated with a file or directory; see pathconf(2).

The <limits.h> header has been standardized by at least three entities.

## ISO Limits

The limits defined by the ISO/IEC 9899:1999 (“ISO C99”) standard are all compile-time limits. The numerical (integer) limits are:

Constant | Type | Minimum value
CHAR_BIT | char | 8
SCHAR_MAX | signed char | 127
SCHAR_MIN | signed char | -127
UCHAR_MAX | unsigned char | 255
INT_MAX | int | 32767
INT_MIN | int | -32767
UINT_MAX | unsigned int | 65535
SHRT_MIN | short | -32767
SHRT_MAX | short | 32767
USHRT_MAX | unsigned short | 65535
LONG_MAX | long int | 2147483647
LONG_MIN | long int | -2147483647
ULONG_MAX | unsigned long int | 4294967295
LLONG_MAX | long long int | 9223372036854775807
LLONG_MIN | long long int | -9223372036854775807
ULLONG_MAX | unsigned long long int | 18446744073709551615
MB_LEN_MAX | - | 1

All listed limits may vary across machines and operating systems. The standard guarantees only that the implementation-defined values are equal or greater in absolute value to those shown. The values permit a system with 16-bit integers using one's complement arithmetic.

Depending whether the system defines char as signed or unsigned, the maximum and minimum values are:

Constant | Type | Minimum value
CHAR_MAX | char | either SCHAR_MAX or UCHAR_MAX
CHAR_MIN | char | either SCHAR_MIN or 0

The two special cases, CHAR_BIT and MB_LEN_MAX, define the number of bits in char and the maximum number of bytes in a multibyte character constant, respectively.

## POSIX Limits

The POSIX.1 standard specifies numerous limits related to the operating system. For each limit, a separate constant prefixed with “_POSIX_” defines the lowest value that the limit is allowed to have on any POSIX compliant system. For instance, _POSIX_OPEN_MAX defines the minimum upper bound permitted by POSIX for the number of files that a single process may have open at any time. This ensures that a portable program can safely reach these limits without prior knowledge about the actual limits used in a particular system.

As the limits are not necessary invariant, pathconf(2) and sysconf(3) should be used to determine the actual value of a limit at runtime. The manual pages of these two functions also contain a more detailed description of the limits available in NetBSD.

## XSI Limits

Also the X/Open System Interface Extension (XSI) specifies few limits. In NetBSD these are limited to LONG_BIT (the number of bits in long), WORD_BIT (the number of bits in a “word”), and few limits related to float and double.

# SEE ALSO

getconf(1), pathconf(2), sysconf(3), types(3), unistd(3)

Richard W. Stevens and Stephen A. Rago, Advanced Programming in the UNIX Environment, Addison-Wesley, Second Edition, 2005.

August 9, 2011 | NetBSD 7.2